EP2698913A1 - Circuit for starting an electric motor within a hand held device - Google Patents

Abstract

The invention relates to a circuit for starting up an electric motor (2) in a handheld implement (1), in particular for a DC motor (100), consisting of a main circuit (11) with the electric motor (2), a battery pack (3) as an energy source and an operating switch (4) for starting the electric motor (2), and a parallel branch to the battery pack (3) and the operating switch (4), wherein in the parallel branch, a capacitor (14) is arranged. In order to reduce the electrical contact load of the operating switch, it is provided to arrange in parallel branch a lying in series with the capacitor (14) electronic switch (15). The series circuit (16) comprising the capacitor (14) and the electronic switch (15) has a first end (16a) and a second end (16b), the ends (16a, 16b) being the only electrical power connection of the capacitor (14 ) to the main circuit (11). The electronic switch (15) of the series circuit (16) will apply only after a period of time after closing the operating switch (4) to the capacitor (14) provided by the battery pack (3) supply voltage.

Description

The invention relates to a circuit for starting up an electric motor in a hand-held implement according to the preamble of claim 1.

Circuits for the commissioning of electric motors in hand-held implements are well known and consist essentially of a main circuit with the electric motor, a battery pack as an energy source and an operating switch for commissioning the electric motor. In order to cover a short-term increased power demand of the electric motor, it is known to arrange a capacitor in parallel to the electric motor or parallel to the battery pack and the operating switch, which provides a portion of the motor current in special operating cases.

If a battery-powered implement is taken after a long break in operation from hibernation in operation, the control electronics is woken up with the closing of the operating switch and charged at the same time the lying in parallel branch capacitor. Due to the high charging current of the capacitor, a considerable electrical switching load of the operating switch occurs. In a mechanical operation switch wear due to the contact bounce the contacts reinforced.

The invention has the object of providing a known circuit for starting an electric motor in such a way that the electrical switching load of the operating switch is reduced when you turn on the implement.

The object is solved according to the characterizing features of claim 1.

In the parallel branch, an electronic switch is installed in series with the capacitor, said series circuit of the capacitor and the electronic switch having a first end and a second end. These ends are connected to the main circuit, so that the charging and discharging of the capacitor flows exclusively over the ends of the series circuit. The electrical power connection of the capacitor to the main circuit is thus formed exclusively over the two ends of the series connection.

The switch located in the series connection of the parallel branch is taken according to the invention only after a period of time after closing the operating switch in the main circuit via a drive circuit in operation to apply to the capacitor provided by the battery pack supply voltage. In this case, the electronic switch of the series circuit connected in series with the capacitor can be operated as an on / off switch or can be slowly opened up over a period of time in order to avoid a sudden current load on the components.

By the circuit according to the invention, the electrical switching load of the operating switch is significantly reduced at the time of switching, so that switching cycles of more than 50,000 switching operations are possible nondestructive. In this case, the time span until the switching-on of the electronic switch of the series connection is advantageously chosen such that the contact bounce characteristic of a mechanical switch has subsided, that is, the contacts abut one another in peace.

In a preferred embodiment, the electronic switch is in the ground branch of the capacitor, d. h., the electronic switch is in the electrical connection between the ground terminal of the capacitor and the ground of the circuit; It may be appropriate to provide the electronic switch on the high side of the capacitor, ie in the electrical connection of the positive pole of the capacitor to the positive pole of the battery pack.

The capacitor is preferably an electrolytic capacitor; the design as a double-layer capacitor, film capacitor or the like. Is also appropriate.

The capacitor has a capacity of more than 10 μF, in particular the capacitor has a capacity of between 100 μF and 5,000 μF. Even with very large capacities of up to 5,000 μF, a disproportionately high switching load of the operating switch is avoided by the inventive design of the circuit.

The operating switch is preferably a mechanical on / off switch; expedient, the mechanical switch can also be designed as a proportional switch with a characteristic between the off position and the full load position.

The electronic switch of the series circuit is in particular a power transistor, preferably a MOSFET, a bipolar transistor or a corresponding power switch. In order to further reduce the current load of the operating switch when switching on and the electrical load on other components, it is not intended to jump through the electronic switch of the series circuit after the period of time, but to control the electronic switch in a predetermined time from the locked position to the fully engaged position ,

The supply voltage applied to the capacitor is expediently the battery voltage; It may be advantageous to design the supply voltage smaller than the battery voltage via a voltage divider or the like.

If the mechanical operating switch remains switched on, then it is provided that the electronic switch of the series circuit separates the capacitor from the supply voltage after detection of an electrical operating state and expiry of a time span. Thus, the drive circuit z. B. determine via their power supply, if the battery voltage falls below a critical limit; this condition occurs, it is detected and separated after a period of time, the capacitor of the series circuit of the supply voltage, so that z. B. over the capacitor no leakage current can flow. As a result, the use of cost-effective capacitors with high leakage currents is possible, whose application is otherwise impractical.

In a preferred embodiment, the circuit according to the invention in a mechanically commutated DC motor, that is provided in a DC motor; It may be expedient to provide the circuit in conjunction with an electronically commutated electric motor.

Fig. 1

eine perspektivische Ansicht auf ein handgeführtes Arbeitsgerät am Beispiel eines Kehrgerätes,

Fig. 2

eine Draufsicht auf das Kehrgerät nach Fig. 1,

Fig. 3

ein Prinzipschaltbild für einen elektrischen Motor als Antriebsmotor in einem handgeführten Arbeitsgerät,

Fig. 4

eine schematische Ansicht einer elektrischen Motorkettensäge,

Fig. 5

eine perspektivische Ansicht einer elektrischen Heckenschere,

Fig. 6

eine Seitenansicht eines elektrischen Blasgerätes,

Fig. 7

ein schematisches Schaltbild zum Betrieb eines elektronisch kommutierten Motors als Antriebsmotor in einem Arbeitsgerät,

Fig. 8

ein schematisches Schaubild zum zeitlichen Ablauf der Betriebsspannung U und des Betriebsstroms I_A über den Betriebsschalter.

Further features of the invention emerge from the further claims, the description and the drawing, in which embodiments of the invention described in detail below are illustrated. Show it:

Fig. 1

a perspective view of a hand-held implement on the example of a sweeping device,

Fig. 2

a plan view of the sweeper after Fig. 1 .

Fig. 3

a schematic diagram of an electric motor as a drive motor in a hand-held implement,

Fig. 4

a schematic view of an electric motor chainsaw,

Fig. 5

a perspective view of an electric hedge trimmer,

Fig. 6

a side view of an electric blower,

Fig. 7

a schematic circuit diagram for operating an electronically commutated motor as a drive motor in a working device,

Fig. 8

a schematic diagram of the timing of the operating voltage U and the operating current I _A via the operating switch.

That in the Figures 1 and 2 illustrated implement 1 is a sweeping device 20 which rests on wheels 21 on the ground and in the front region about vertical axes rotating cleaning brush 22 as working tools. The rotating cleaning brushes 22 carry detected dirt into a rear sump 23.

In the front housing area a rotary knob 24 is provided for adjusting the height of the implement 1 between the cleaning brushes; between the knob and the reservoir 23, a battery compartment 25 is formed in the housing, in which a battery pack 26 is inserted. Between the battery compartment 25 and the collecting container 23, an operating switch 4 is provided in the housing, which as a mechanical switch 10 (FIG. Figures 3 . 7 ) is trained.

The sweeper 20 further includes a bow handle 27 for guiding the implement 1, which is U-shaped and is fastened with its leg ends on the housing of the sweeping device.

The electric motor used as the drive motor of the implement 1 is taken over the mechanical switch 10 in operation. The in Fig. 3 shown electric motor 2 is a DC motor 100. The electric motor 2 is located in the main circuit 11 of a circuit shown 7 for putting the electric motor 2. The main circuit 11 is made essentially from the electric motor 2, a battery pack 3 as an energy source 9 and the operating switch 4, which is designed as a manually operated, mechanical switch 10, in particular as a mechanical on / off switch.

Are to drive the cleaning brush 22 a plurality of electric motors arranged, for. B. for each cleaning brush 22 an electric motor, the electric motors are electrically connected in parallel to each other, as in Fig. 3 is shown in dashed lines. The circuit 7 itself remains unchanged.

The battery pack 3 is formed from individual cells 3.1, 3.2, 3.3 to 3.n, wherein the individual cells can lie in rows and / or parallel to each other.

In the embodiment shown, an electronic power switch 5 is also provided in the main circuit 11 on the high side of the electric motor 2, ie on the side of the positive pole, which is formed in the embodiment shown as a MOSFET 6. The control connection or the gate 8 is connected via a control line 12 to a drive circuit 13. It may be expedient to provide the electronic power switch 5 instead of on the high side of the electric motor 2 on the low side of the electric motor 2, ie on the side of the ground connection.

Parallel to the electric motor 2 is also an electronic power switch 35, which is advantageously designed as a MOSFET 36. The power switch 35 is parallel to the electric motor 2 and serves as a freewheeling path when switching inductive loads; Advantageously, the outflow time of the motor 2 can be lowered via the freewheeling path when the operating switch 4 is open. The gate 38 is connected to the drive circuit 13 via the control line 37.

The circuit 7 further comprises a series circuit of a capacitor 14 and an electronic switch 15, wherein the series circuit 16 is located as a parallel branch to the circuit breaker 5 and the electric motor 2 in the main circuit 11. The electronic Switch 15 is advantageously provided in the ground branch of capacitor 14, that is, in the electrical connection between the negative pole of capacitor 14 and the ground terminal of circuit 7 or the negative terminal of battery pack 3.

The series circuit 16 has a first end 16a and a second end 16b. These ends 16a and 16b represent the only direct electrical power connection of the capacitor 14 to the main circuit 11.

The control terminal (gate 17) of the electronic switch 15 preferably designed as a MOSFET 19 is connected to the drive circuit 13; This indirect connection with the main circuit 11 is not a power connection, since no significant charging or discharging current of the capacitor 14 flows via the control terminal 17. The electrical charging and discharging currents of the capacitor 14 flow through the ends 16a and 16b of the series connection, so that the ends 16a, 16b represent the only electrical power connection of the capacitor 14 to the main circuit 11. The drive circuit 13 controls suitably also other electronic power switches 5, 35 of the circuit. 7

The drive circuit 13 detects the switching on of the mechanical operating switch 4 z. B. via its own power supply 18 or a signal line 33, via which the drive circuit 13, the switching position of the operating switch 4 is communicated.

If the user switches manually via the mechanical operating switch 4 at the time t ₀ (FIG. Fig. 8 ) the main circuit 11 of the circuit 7, so first the control electronics is woken up, so the drive circuit 13 is put into operation. In this case, a small operating current I _{B occurs} over a time t ₁ , as in Fig. 8 is shown. This small operating current I _B is switched by the operating switch 4, in particular, this is only this small operating current I _B during the period t _K = t ₂ - to the contact bounce of the mechanical switch 10 at. Contact bounce occurs at each mechanical switch 10 and designates the period of switching from the off-state to the on-state, in which rest the contacts of the operating switch 4 and the mechanical switch 10 at rest to each other.

After expiration of a predetermined period of time t ₃ -t ₀ , which may be in a range of 1 to 300 milliseconds, preferably in the range of 1 to 50 ms, the drive circuit 13 controls at time t ₃ (FIG. Fig. 8 ) The electronic switch 15 in the series circuit 16, in the embodiment, the gate 17 of the MOSFET 19, so that the switch 15 completely or partially turns on and thus in the series circuit 16 as a parallel branch to the battery pack 3 and the operating switch 4, a current I _C flows ; the capacitor 14 charges to the voltage U _C. On the capacitor 14 is a supply voltage, which is preferably the battery voltage U _A.

Since the MOSFET 19 closes by a time period of about 1 ms to 50 ms, advantageously about 10 ms, delayed after pressing the operating switch 4, preferably the contact bounce is substantially or completely subsided and the charging current I _{C of} the capacitor 14, the Do not load the operating switch 4 at the time of switching on and during the contact bounce. If the electric motor 2 - preferably via a circuit breaker 5 - z. B. taken at time t ₄ in operation, the charging current I _{C of} the capacitor 14 has already dropped. Advantageously, the charging current I _C through the capacitor 14 does not lead to an increased electrical load of the battery pack 3 in addition to the motor current I _M. The current I _A taken from the battery pack 3 is thus at a time after the time t ₄ after the operation switch 4 has been switched on Essentially, the motor current I _M be. The through-connected by the drive circuit 13 electronic switch 5, so the MOSFET 6 is controlled by the gate 8 and closes the main circuit 11; through the DC motor 100, the motor current I _{M flows} ; the electric motor 2 rotates and drives the working tool of the implement 1.

The drive circuit 13 according to Fig. 3 with a DC motor 100 as a drive motor for a working tool can be used in many battery-powered implements 1, as they are exemplified in the FIGS. 1, 2 and 4 to 6 are shown.

Fig. 4 shows a power tool 1, a power saw 40, in the housing, a battery compartment 45 is formed. In the battery bay 45, a battery pack 46 is inserted, which is formed from arranged in a battery housing individual cells 3.1 to 3.n as a battery pack 3.

The power saw 40 has a rear handle 41, which is aligned in the longitudinal direction of the implement 1, and a bow handle 42, which is arranged in the front region of the housing and lies transversely to the longitudinal direction, as a front handle. The battery bay 45 is located between the bow handle 42 and the rear handle 41, wherein the operating switch 4 is provided for the intended as a drive motor in the housing electric motor 2 in the rear handle 41. The operating switch 4 is not provided as an on / off switch, but as a position-proportional throttle, which emits a signal to the drive circuit 13 depending on the executed travel. Depending on the travel, the rotational speed of the electric motor 2 ( Fig. 3 ) controlled.

This in Fig. 5 illustrated implement 1 is a hedge trimmer 50 with a rear, aligned in the longitudinal direction of the implement 1 rear handle 51, wherein in the front region of the housing a transverse to the longitudinal direction bow handle 52 is arranged as a front handle. The front bow handle 52 is formed as a double-shell handle, wherein the two partial shells are movable relative to each other and z. B. operate a switch a two-hand safety.

Between the front bow handle 52 and the rear handle 51, a battery compartment 55 is formed in the housing of the hedge trimmer 50, in which a battery pack 56 is inserted as an energy source.

In the rear handle 51 of the hedge trimmer, the operating switch 4 is arranged, which is designed as an on / off switch.

Another implement 1 is in Fig. 6 represented and designed as a blower 60. The housing of the blower 60 has a longitudinal direction of the implement 1 aligned handle 61, which is executed in the embodiment shown as an upper handle. In the housing, a suction port 63 is provided, which lies below the handle 61; the blowing air flow generated by a blower is discharged through a blowpipe 64 to the front.

At the rear end of the handle 61, a housing extension 67 is provided which extends in the longitudinal direction of the working device 1 and forms a battery compartment 65. In the battery compartment a battery pack 66 is inserted as an energy source.

The illustrated, battery-powered implements 1 show examples of electrical equipment in which the circuit according to the invention can be advantageously applied. As tools are also battery-powered cut-off grinder, rechargeable battery-operated blower devices, brushcutters, Emtegeräte or the like. Expedient.

In the embodiment according to Fig. 7 is schematically the circuit according to the invention according to Fig. 3 for an embodiment of the electric motor 2 as an electronically commutated motor 200 (EC motor) reproduced. The same components, circuits and signal lines are denoted by the same reference numerals as in Fig. 3 designated.

The electronically commutated electric motor 200 is controlled via a drive bridge 201, wherein the drive bridge converts a battery voltage U _A into the three phases U, V and W for the EC motor 200. For this purpose, three parallel branches are provided in the drive circuit, in each of which two MOSFETs 6.1, 6.2; 6.3, 6.4; 6.5, 6.6 are arranged. The phase terminals U, V and W are tapped between each two MOSFET's a parallel branch; the phase U is tapped between the MOSFETs 6.1 and 6.2, the phase V between the MOSFETs 6.3 and 6.4 and the phase W between the MOSFETs 6.5 and 6.6.

The control terminals (gate) of the MOSFETs are controlled via control lines 12.1 to 12.6 of the drive circuit 13, which also controls the MOSFET 19 of the series circuit 16 of capacitor 14 and MOSFET 19 via the control line 17. In addition, the operating state of the operating switch 4 is communicated to the drive circuit 13 via the signal line 33.

It may be expedient to provide a control circuit 13a separate from the drive circuit 13 for driving the electronic switch 15 in the series circuit 16 and to execute the bridge control 13b separately therefrom. It is advantageously provided to control the control circuit 13a and the bridge controller 13b by a microprocessor 30, the circuits and the microprocessor 30 advantageously being combined together in the drive circuit 13.

The capacitor 14 of the series circuit 16 may be a single capacitor of any type ( Fig. 3 . 7 ), z. As a double-layer capacitor, a film capacitor, an electrolytic capacitor or the like .. Preferably, the invention is carried out with an electrolytic capacitor. As a capacitor, series circuits or parallel circuits of components of the same or different capacities can be provided.

The capacitor 14 used has a capacity of more than 10 μF, in particular, the capacitance of the capacitor 14 is in the range of 100 μF to 5000 μF.

In the illustrated embodiment, the electronic switch 15 of the series circuit 16 is a power transistor. This is preferably not switched abruptly from the blocking position to the fully conductive position, but turned on within a predetermined control time, so that the charging current increases in a controlled manner. Thereby, the peak current load of the components of the circuit and also the electrical load of the battery pack 3 can be lowered.

In practice, it may happen -. B. in the sweeper after the Figures 1 and 2 - That the mechanical operation switch 4 remains in its on position, since the user uses the sweeping device until due to the sunken battery voltage, the drive circuit 13 turns off the electric motor. If this condition occurs, this operating state -. B. by falling below a battery backup voltage - detected and separated after this state detection and expiration of a predetermined period of time, the capacitor of the series circuit of the supply voltage, so that the design-related leakage current through the capacitor does not lead to a total discharge and possible damage to the battery pack.

The battery pack 3 of individual cells 3.1, 3.2, 3.3 to 3.n is preferably a lithium-ion battery pack; Other versions that are chemically based on lithium, such. As lithium polymer, lithium iron or the like. Are appropriate. In the battery pack 3, individual cells 3.1 to 3.n of any number, type and any chemical structure can be connected together to form an energy source 9.

In the diagram after Fig. 8 As an exemplary embodiment, a time sequence for switching on a working device is reproduced. At time t ₀ , the operating switch 4, preferably a mechanical on / off switch 10 is turned on, whereby the battery voltage U _A to the circuit 11 and the drive circuit 13 is applied. It occurs on a first operating current I _B , which is received by the drive circuit 13. The operating current I _B is switched as a switching current from the operating switch 4 and is also during the period t _{k of} the contact bounce. After the contact bounce of the operating switch 4 has disappeared, the series connection 16 is switched through at the time t ₃ , which is approximately 1 ms to 50 ms after the time t ₀ of switching on, so that the capacitor 14 charges and a charging current I _C flows. After charging the capacitor 14 - the charging current I _C is preferably decayed - the electric motor 2 is switched on at the time t ₄ , so that the motor current I _M flows. The time t ₄ is in a range of about 1 ms to 300 ms after the time t ₀ , the time of switching on of the manual operation switch 4. Between the time t ₀ of switching on the manual operation switch 4 and the turning on of the motor current I _M at time t ₄ , the time t _G of 1 ms to 300 ms.

Claims (12)

Circuit for starting an electric motor (2) in a hand-held implement (1), in particular for a DC motor (100), consisting of a main circuit (11) with the electric motor (2), a battery pack (3) as an energy source and a mechanical operating switch ( 4) for starting the electric motor (2), and a parallel branch to the battery pack (3) and the operating switch (4), wherein in the parallel branch, a capacitor (14) is arranged,
characterized in that the parallel branch comprises an electronic switch (15) in series with the capacitor (14), that the series circuit (16) of the capacitor (14) and the electronic switch (15) has a first end (16a) and a second end (16b), and the ends (16a, 16b) constitute the only electrical power connection of the capacitor (14) to the main circuit (11) and that the electronic switch (15) of the series circuit (16) after a lapse of time the closing of the operating switch (4) to the capacitor (14) from the battery pack (3) provided supply voltage applies. Circuit according to Claim 1,
characterized in that the electronic switch (15) in the ground branch of the capacitor (14). Circuit according to Claim 1 or 2,
characterized in that the capacitor (14) is an electrolytic capacitor. Circuit according to one of Claims 1 to 3,
characterized in that the capacitor (14) has a capacitance of more than 10 μF. Circuit according to Claim 4,
characterized in that the capacitance of the capacitor (14) is in the range of 100 μF to 5,000 μF. Circuit according to one of claims 1 to 5, characterized
characterized in that the operating switch (4) is a mechanical on / off switch (10). Circuit according to one of Claims 1 to 6,
characterized in that the electronic switch (15) of the series circuit (16) is a power transistor, in particular a MOSFET (19). Circuit according to one of claims 1 to 7,
characterized in that the electronic switch (15) is controlled in a predetermined control time from its blocking position to a conductive position. Circuit according to one of Claims 1 to 8, characterized
characterized in that the supply voltage is the battery voltage (U _A ). Circuit according to one of claims 1 to 9,
characterized in that the electronic switch (15) of the series circuit (16) separates the capacitor (14) after detection of an electrical operating condition and expiration of a period of time from the supply voltage. Circuit according to one of Claims 1 to 10,
characterized in that the electric motor (2) is an electronically commutated electric motor (200). Circuit according to one of Claims 1 to 10,
characterized in that a plurality of electric motors are provided and the electric motors (2) are mechanically commutated electric motors, wherein the electric motors (2) to each other electrically connected in parallel in the main circuit (11).

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